Although it is well known in the art of filtration to clean filter elements by passing fluid in a reverse direction through the filter elements, the use of this method for cleaning high temperature gas filters has not been successful in some applications where a very fine filter cake adheres to the filter element in a particularly tenacious manner. This is known to occur, for example, where the gas contains an undue amount of moisture so that the cake is relatively wet.
It is known to blow high velocity pulses of gas directly into the outlet side of a bank of filter tubes to momentarily cause a reverse flow of gas through some or all of the filter elements while the filter remains on line. However, in some cases the cleaning gas thus introduced into the filter tubes does not penetrate the walls of the filter elements but takes the path of least resistance and simply flows with the main gas stream out through the gas outlet port of the filter. Attempts to solve this problem have included such things as taking the filter off line during the cleaning operation or closing the outlet ports of a selected number of filter tubes while the high velocity cleaning gas is supplied to the downstream sides of the filters. While such techniques result in better cleaning operations, it would be still better if the cleaning operation could be carried out while the entire filter remains on line and without closing the outlet line from the filter tubes being cleaned. Also in high temperature applications it may be difficult to provide a valve or other means of closing off the filter outlet.